Oscillation Transfer Mechanism in Grid-Forming Virtual Synchronous Generator Systems
The integration of high-penetration renewable energy sources into power grids has exacerbated deficiencies in system inertia and damping, precipitating sub-synchronous oscillation (SSO) instabilities. Grid-forming virtual synchronous generator (GFM-VSG) systems, which emulate the rotor inertia and damping characteristics of conventional synchronous machines, are increasingly deployed to provide grid support. This study establishes an oscillation transfer effect model and evaluation framework to elucidate the mechanisms by which oscillations propagate among electrical quantities in GFM-VSG systems. The analysis reveals that SSO in GFM-VSG systems does not solely arise from insufficient stability margins; it is also attributable to oscillation transfer effects between different electrical quantities. The proposed framework enables quantitative assessment of oscillation transfer effects. Experimental validation confirms the effectiveness and feasibility of the modeling methodology and evaluation framework. The oscillation transfer model's amplitude-frequency characteristic at the oscillation frequency directly reflects the strength of oscillation transfer between corresponding electrical quantities, and experimental results align with this characteristic. The findings demonstrate that conventional stability analysis models, which neglect oscillation transfer effects, are inadequate for capturing the coupling mechanisms that influence system stability. The proposed framework provides a systematic approach to quantify these effects, thereby enabling targeted suppression of SSO and enhancement of system stability.